Field of the Disclosure
The present disclosure relates generally to controllers for switched mode power converters and specifically relates to power converters having both an input-side and an output-side controller where the output-side controller communicates a switching request signal to the input-side controller via an isolation barrier to control an input-side switch.
Background
Switch mode power converters are widely used for household or industrial appliances that require a regulated direct current (dc) source for their operation, such as for example battery chargers that are commonly used in electronic mobile devices. Off-line ac-dc converters convert a low frequency (e.g., 50 Hz or 60 Hz) high voltage ac (alternating current) input voltage to a required level of dc output voltage. Various types of switch mode power converters are popular because of their well regulated output, high efficiency, and small size along with their safety and protection features.
Safety requirements for isolated switch mode power converters generally require the use of high frequency transformers to provide galvanic isolation between the inputs and outputs of the switch mode power converters in addition to the voltage regulation at the output. Popular topologies of isolated switch mode power converters may include flyback, forward, isolated half/full bridge, among many others including resonant types.
One source of loss in switch mode power supplies is the switching loss during turn on and turn off of the power switch. In an isolated switch mode power converter High Frequency (HF) turn on oscillations may happen due to resonance between the leakage inductance of the transformer and the output capacitance of the power switch (e.g., total parasitic capacitance across the power MOSFET). In discontinuous current mode DCM operation of an isolated switch mode power converter, in addition to above mentioned HF turn on oscillations, a second lower frequency oscillation may also happen between the magnetic inductance of the transformer and the output capacitance of the power switch. This second lower frequency oscillation may often be referred to as a quasi resonance (QR) mode of operation. One method of reducing the turn ON losses in an isolated DCM switch mode power converter is the quasi resonant valley switching of the power switch, where an input parameter, such as switch current, is directly monitored so that a voltage across the input-side switch is at or near a minimum when the input-side switch is turned ON.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.